This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-170036, filed Jun. 16, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to electronic apparatus using batteries as a drive source, and in particular, to battery-driven apparatus having a battery exhaustion determining function for apparatus such as cameras.
Today, various dry batteries are commercially available. Image pickup devices, for example, cameras generally use as a power supply, lithium (Li) batteries, which have a large capacity and whose internal resistance or open voltage does not vary rapidly despite exhaustion.
For example, electronic apparatus such as remote control devices for televisions and radios or radio cassettes commonly use size D to A alkaline or manganese batteries, but these batteries are more inexpensive and popular than the lithium batteries. These alkaline or manganese batteries are sold at many stores such as convenience stores and station kiosks.
Thus, camera users prefer cameras that allow the use of size B or A batteries for replacements, which are readily available and inexpensive. Since, however, these size D to A batteries can be manufactured easily, they are manufactured in many countries and by various manufacturers and have different characteristics.
Such characteristics include the number of frames that can be photographed by a camera before batteries are exhausted and must be replaced with new ones. Even if a camera uses batteries from a battery manufacturer observing a predetermined standard, if the camera user replaces these batteries with ones from a different manufacture having different characteristics, the number of frames that can be photographed during the lifetime of the batteries changes. As a result, performance achieved by the camera depends heavily on the operating batteries.
Compared to the lithium batteries, the alkaline batteries have small variations in voltage even when exhausted, as shown in FIG. 14. Accordingly, level setting is difficult in determining whether or not the batteries have been consumed to the extent that the camera cannot be operated. Without the display of a warning indicating that, for example, an incorrect level setting causes the camera to malfunction, the user does not know when to replace the batteries, thereby missing perfect moments for good photographs.
In addition, different alkaline battery manufactures use significantly different internal resistances or temperature conditions. Accordingly, without the accurate knowledge of such differences, it is impossible to check beforehand whether or not the camera operates correctly.
In contrast, since a camera with lithium batteries does not have the internal resistance of the batteries varying rapidly, the batteries are effectively checked using a circuit configured, for example, as shown in FIG. 15.
In FIG. 15, reference numeral 101 denotes an equivalent circuit for batteries which takes their internal resistance into consideration. Reference numeral 6 denotes a site of the camera which is driven by the batteries, for example, a shutter or a winding movable mechatornic section actuated by an actuator such as a plunger or a motor. A predetermined current Is or higher must be conducted through these actuators before they can be operated.
When the amount of required current is defined as Is, a voltage Vs is applied to the mechatronic section 6 as shown in:
Vs=V0xe2x88x92ZIsxe2x80x83xe2x80x83(1)
If, for example, a mechanism such as a shutter is checked for opening and closing operations before photographing, unwanted image pick-up or film exposure may result. Thus, an alternative means must be used to maintain correct operations based on the battery voltage. Thus, the correct operations are conventionally maintained by turning on a current source 17 to provide a checking dummy current ID and determining the resulting battery voltage Vc.
In this case, the following equation holds:
Vc=V0xe2x88x92ZIDxe2x80x83xe2x80x83(2),
so that with the above Equation (1), the following equation holds:
Vc=Vs+ZIsxe2x88x92ZID=Vs+Z(Isxe2x88x92ID)xe2x80x83xe2x80x83(3)
Further, since the Is, ID, and Z are known, a required voltage Vs can be determined from Vc using the following Equation (4):
Vs=Vcxe2x88x92Zxc2x7(Isxe2x88x92ID)xe2x80x83xe2x80x83(4)
That is, with conventional cameras, by monitoring the battery voltage Vc effected when the dummy current ID is conducted, whether or not the battery voltage is sufficient to actuate the mechatronic section 6 can be determined. That is, the battery check can be performed. The determination based on Equation (4), however, is ineffective on batteries with a varying Z.
To solve such a problem, conventional documents, for example, Jap. Pat. Appln. KOKAI Publication No. 7-64146 and U.S. Pat. No. 5,701,527 disclose techniques for improving battery check timings or loads attended with battery checks or the like to maximize the performance of the batteries.
However, the techniques disclosed by Jap. Pat. Appln. KOKAI Publication No. 7-64146 and U.S. Pat. No. 5,701,527 are only applications of the above Equation (4) and fail to take into account a voltage recovery effect of the batteries, which is a particular characteristic of the alkaline batteries.
Due to this voltage recovery effect, when batteries that have been determined to be exhausted are left for a certain period of time, they may instantaneously exhibit characteristics similar to those of new batteries because chemical reaction within the batteries changes during this period in a manner such that their voltage appears to be recovered.
The alkaline battery will be described below with reference to FIG. 16 showing a sectional view thereof.
As shown in this figure, an armor 207 houses a vessel 203 that seals a positive-electrode mix 205 and a gelated negative-electrode zinc 202 that are separated by a separator 206 comprising a non-woven cloth so that manganese dioxide and an electrolyte contained in the positive-electrode mix 205 react to zinc in the negative electrode to generate an electromotive force. Reference numeral 201 denotes a terminal plate. Reference numerals 204, 208 denote an insulating ring. Reference numeral 209 denotes a bottom plate. Reference numeral 210 denotes a negative-electrode collector.
After this reaction, a reactant remains in the electrolyte to increase the internal resistance of the batteries. Consequently, a discharge characteristic of the alkaline battery is as shown in FIGS. 3A and 3B; that is, the internal resistance increases as the discharge progresses. Once the discharge stops, however, the progressing chemical reaction is partly cleared to exhibit a xe2x80x9crecovery characteristic (the voltage recovery effect)xe2x80x9d. If these batteries are checked for exhaustion, the result will be incorrect. That is, the batteries are shown to be new though they must actually be replaced with new ones.
Such a mistaken determination causes the user to miss the chance of replacing the batteries, so that a warning may appear or photographing may be disabled immediately after the start of actual photographing, thereby making the user panic. In particular, an irreparable situation may occur if such a mistaken determination is made before occasions such as travel and a wedding ceremony when many photographs are taken.
The present invention is provided in view of the above problems, and it is an object thereof to check batteries taking their recovery characteristic (the voltage recovery effect) into consideration to urge a user to replace the batteries with new ones at an appropriate time in order to avoid the worst situation where the user miss perfect moments for good photographs.
To attain this object, a first aspect of the present invention provides electronic apparatus using removable batteries as a drive source, the apparatus comprising a display section for showing how the batteries are consumed, a determination circuit for detecting internal resistance value of the batteries and using this value to determine how the batteries are consumed, a memory that stores a result of the determination made by the determination circuit, and a control circuit for controlling the contents of the display on the display section depending on the current determination result information from the determination circuit and on the past determination result information stored in the memory.
A second aspect of the present invention provides electronic apparatus using removable batteries as a drive source, the apparatus comprising a display section for showing how the batteries are consumed, a first memory that stores a current value and a voltage value required for camera operations, a determination circuit for detecting a internal resistance value of the batteries and using this value and the current and voltage values stored in the first memory to determine how the batteries are consumed, and a control circuit for controlling the contents of the display on the display section depending on a result of the determination made by the determination circuit.
A third aspect of the present invention provides electronic apparatus using removable batteries as a drive source, the apparatus comprising decision means for deciding a timing used to determine a battery state, determination means for using the determination timing decided by the decision means, to determine the battery voltage, temperature measuring means for measuring a temperature of the batteries or a periphery thereof, storage means for storing a result of the determination made by the determination means and a temperature measurement result from the temperature measuring means, display means for showing how the batteries are consumed, and display control means for deciding the contents of the display on the display means to control the display means based on the information stored in the storage means.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.